Embodiments of the present disclosure provide a cover assembly that includes a cover disposed between a device side surface of a substrate and a reflector plate, which are disposed within a thermal processing chamber. The presence of the cover between the device side surface of a substrate and a reflector plate has many advantages over conventional thermal processing chamber designs, which include an improved temperature uniformity during processing, a reduced chamber down time and an improved cost-of-ownership of the processes performed in the thermal processing chamber. In some configurations, the cover includes two or more ports that are formed therein and are positioned to deliver a gas, from a space formed between the reflector plate and the cover, to desired regions of the substrate during processing to reduce the temperature variation across the substrate.